This secondary common control physical channel (S-CCPCH) is known to be a physical common channel on the downlink that may carry basically two transport channels, namely the paging channel (PCH) and the forward access channel (FACH). The S-CCPCH is therefore used for paging and for transmission of signalling bits or quite small amount of data. There may be one or several S-CCPCHs in each cell with different gross bit-rates in function of the traffic load on this physical channel.
The S-CCPCH is a physical channel comprising frames which are subdivided into time slots, each time slot is having a data field for inserting useful data bits, namely data bits of the transport channels PCH and/or FACH. As a result from this the S-CCPCH is able to carry zero or one PCH transport channel and zero, one or several FACH transport channels. These different combinations of the transport channels are called TFC (transport format combinations). The possible TFCs do also include the case that temporally no data at all is transmitted on the S-CCPH. In order to indicate the used TFC there is defined a so-called TFCI (TFC identification) which is a number indicating the used TFC.
The TFCI bits are transmitted in a field within the slots of the S-CCPCH frame, so that all mobile stations, i.e. user equipments (UEs), within the radio cell can know the currently used TFC.
Further to this there are so-called pilot bits which are inserted in a further field of the slots, these pilot bits are representing a bit pattern for constituting a pilot signal which allow at the receiving end, i.e. at the UE, to optimize the equalization of the data received on the S-CCPCH.
At the transmitting end, i.e. at the base station, the transmit power level to be used for data bits transmitted on the S-CCPCH is controlled by a radio network controller (RNC) which is connected to that base station. The transmit powers for the TFCI bits and Pilot bits which may be different are also controlled by the RNC by adapting these powers relatively to the currently used power of the S-CCPCH data bits.